Projective mems device for a picoprojector of the flying spot type and related manufacturing method

ABSTRACT

A projective MEMS device, including: a fixed supporting structure made at least in part of semiconductor material; and a number of projective modules. Each projective module includes an optical source, fixed to the fixed supporting structure, and a microelectromechanical actuator, which includes a mobile structure and varies the position of the mobile structure with respect to the fixed supporting structure. Each projective module further includes an initial optical fiber, which is mechanically coupled to the mobile structure and optically couples to the optical source according to the position of the mobile structure.

BACKGROUND Technical Field

The present disclosure relates to a projective micro-electro-mechanicalsystem (MEMS) device that may be used, for example, for forming aso-called picoprojector of the flying-spot type; further, the presentdisclosure relates to the related manufacturing method.

Description of the Related Art

As is known, numerous opto-electronic MEMS systems are today available,which are designed to generate images (for example, on correspondingscreens) and are characterized by extremely small volumes; theseopto-electronic MEMS systems are also known as “picoprojectors”. Ingeneral, the volumes of current picoprojectors are so small as to enableinclusion of picoprojectors inside, for example, a cellphone.Picoprojectors may thus form so-called embedded modules of portableelectronic devices, such as for example portable PCs, tablets,cellphones, etc.

A picoprojector generally comprises a corresponding projective device,which includes one or more optical sources and may implement differentoptical techniques.

For instance, the paper by Dawei Rui, et al., “Optical design inillumination system of digital light processing projector using laserand gradient-index lens”, Optical Engineering 51(1) (January, 2012)describes a picoprojector that implements so-called digital lightprocessing (DLP) and includes a plurality of micro-mirrors.

Likewise known are picoprojectors of the flying spot type, which areconfigured to generate, in use, a corresponding optical beam, thedirection of propagation and the spectral composition of which arevaried dynamically, for example by a mirror and one or more drivingcircuits, respectively, so that the optical beam may periodically scan ascreen arranged at a distance, thus generating an image thereon. Anexample of picoprojector of the flying spot type is provided in thepaper by Masafumi Ide, et al., “Compact multiple laser beam scanningmodule for high-resolution picoprojector applications using a fiberbundle combiner”, Advances in Display Technologies IV, Proceedings ofSPIE, Vol. 9005, 90050F-1-12.

In general, projective systems of the flying spot type are characterizedby overall dimensions smaller than those of projective systems of a DLPtype, thanks to the lower complexity.

This having been said, in the field of projective systems of the flyingspot type, there is particularly felt the need to improve the opticalcharacteristics of the optical beam generated, without penalizing theoverall dimensions. As regards the optical characteristics of theoptical beam, they comprise, among other things, power and divergence.In particular, as regards divergence, and assuming an orthogonalreference system xyz, with the axis z coinciding with the axis of theoptical beam emitted, it is known that, in the presence of a differencebetween the divergence of the optical beam in the plane xz and thedivergence of the optical beam in the plane yz, the so-called phenomenonof astigmatism arises; i.e., different components of the optical beamfocus on different points, reducing the quality of the image generated.

BRIEF SUMMARY

One embodiment of the present disclosure is a projective device for apicoprojector of the flying spot type, which enables an at least partialimprovement of one or more of the optical characteristics of the opticalbeam.

According to at least one embodiment of the present disclosure, aprojective MEMS device includes a fixed supporting structure made atleast in part of semiconductor material; and a number of projectivemodules. Each projective module includes an optical source fixed to thefixed supporting structure, a microelectromechanical actuator, and aninitial optical fiber. The microelectromechanical actuator includes amobile structure and is configured to vary a position of said mobilestructure with respect to the fixed supporting structure. The initialoptical fiber is mechanically coupled to said mobile structure andconfigured to optically couple to said optical source according to theposition of said mobile structure.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

For a better understanding of the present disclosure, preferredembodiments thereof are now described, purely by way of non-limitingexample and with reference to the attached drawings, wherein:

FIG. 1 is a schematic perspective view of a portion of an opticalsource;

FIG. 2 is a schematic top plan view of a portion of an embodiment of thepresent projective MEMS device;

FIG. 3 is a schematic cross-sectional view of a portion of an embodimentof the present projective MEMS device;

FIG. 4 is a schematic top plan view of a portion of an embodiment of thepresent projective MEMS device;

FIG. 5 is a schematic top plan view of a portion of an embodiment of thepresent projective MEMS device;

FIG. 6 is a schematic top plan view of an embodiment of the presentprojective MEMS device;

FIGS. 7 and 8 are schematic perspective views of portable apparatusesthat include the present projective MEMS device; and

FIGS. 9-18 are schematic cross-sectional views of portions of anembodiment of the present projective MEMS device, during successivesteps of a manufacturing process.

DETAILED DESCRIPTION

FIG. 1 shows a first optical source, of a per se known type, which isformed by a first laser diode 2, configured to emit electromagneticradiation with a first wavelength λ₁ (for example, in the blue, i.e.,λ₁≈440 nm), referred to hereinafter as the first optical beam B₁. In aper se known manner, the first laser diode 2 is formed by a die 4 ofsemiconductor material, which includes a semiconductor body 3, formedfor example by binary, ternary, or quaternary alloys of semiconductorsIII-V or II-VI (for example, AlGaAs or InGaN). The semiconductor body 3is of a per se known type and includes, among other things, an opticallyactive layer 6, which has the shape of a parallelepiped with a thicknesssmaller than (for example) 0.1 μm and may function as optical guide,inside which there occurs the phenomenon of laser generation. Purely byway of example, in what follows an orthogonal reference system xyz isassumed, arranged so that the optically active layer 6 is parallel tothe plane xz. Further, the die 4 is delimited by a front facet F_(a) andby a rear facet F_(b), which are arranged perpendicular to the axis z.

In a per se known manner, the first laser diode 2 emits the firstoptical beam B₁ starting from the front facet F_(a). For simplicity, inwhat follows it is assumed that the axis of propagation (designated byH₁) of the first optical beam B₁ coincides with the axis z. Furthermore,on the front facet F_(a), the first optical beam B₁ forms a light spotSP, which, without any loss of generality, has for example anapproximately elliptical shape, the axes of which are parallel to theaxes x and y respectively and may range, for example, between 0.5 and 3μm; in the example illustrated in FIG. 1, the spot SP has a geometricalcenter O arranged along the axis z. In addition, at output from thefront facet F_(a), the divergences of the first optical beam B₁ in theplanes xz and yz are markedly different from one another, a fact that,as mentioned previously, could cause the so-called phenomenon ofastigmatism.

In greater detail, and without any loss of generality, the first laserdiode 2 is a so-called bare-chip, i.e., a chip without package. In thisconnection, once again without any loss of generality, the die 4 may beof the type with epitaxy in the respective bottom part and includes abottom region (not illustrated) formed by a solder alloy, whichincludes, for example, gold and is designed to enable, in a per se knownmanner, fixing of the first laser diode 2 to a metal pad of an externalstructure. This bottom region thus also enables thermal dissipation ofthe first laser diode 2, with consequent improvement of performance ofthe latter. Said bottom region may have a thickness, for example, of 3μm.

FIG. 2 (not in scale) shows a portion of a projective MEMS device 10,which includes a so-called silicon optical bench (SiOB), which is madeat least in part of semiconductor material (for example, but notnecessarily, silicon) and functions as support. For this reason, in whatfollows this optical bench is referred to as the semiconductor support16. In addition, the semiconductor support 16 comprises a fixedstructure 17 and a first mobile structure 19, the latter beingrepresented (with a dashed line) in a purely qualitative way in FIG. 2.The details regarding the fixed structure 17 and the operative relationwith the first mobile structure 19 are not shown in FIG. 2 either.

The projective MEMS device 10 further comprises a first single-modeoptical fiber 20 and a first multi-mode optical fiber 22.

The first laser diode 2, the first single-mode optical fiber 20 and thefirst multi-mode optical fiber 22 are coupled to the semiconductorsupport 16, as described in greater detail hereinafter and are opticallycoupled together, so that the first single-mode optical fiber 20 isoptically arranged between the first laser diode 2 and the firstmulti-mode optical fiber 22. Consequently, the first optical beam B₁traverses in succession the first single-mode optical fiber 20 and thefirst multi-mode optical fiber 22. In other words, from the standpointof the first optical beam B₁, the first single-mode optical fiber 20 andthe first multi-mode optical fiber 22 function as initial optical fiberand subsequent optical fiber, respectively.

The first single-mode fiber 20 is delimited by a first facet F₁ and asecond facet F₂ and has a so-called core having a diameter comprised,for example, between 2 μm and 8 μm. Further, the first single-modeoptical fiber 20 has a length comprised, for example, between 300 μm and700 μm. The first facet F₁ faces the front facet F_(a) of the firstlaser diode 2, so that at least a portion of the first optical beam B₁couples to the first single-mode optical fiber 20 through the firstfacet F₁. In this connection, for brevity, in what follows the portionof first optical beam B₁ that couples to the first single-mode opticalfiber 20 will also be referred to as the first optical beam B₁. More ingeneral, given a point of an optical path that connects the first laserdiode 2 to a common output (described hereinafter) and is followed bythe first optical beam B₁, in this point the portion of first opticalbeam B₁ that is to reach the common output will be referred to as thefirst optical beam B₁. In other words, the optical losses are neglected.

In greater detail, in a per se known manner, the first facet F₁ of thefirst single-mode optical fiber 20 may form a corresponding lens of atype known, designed to increase the efficiency of optical couplingbetween the first laser diode 2 and the first single-mode optical fiber20. In other words, the first single-mode optical fiber 20 may be aso-called “lensed fiber”. The second facet F₂ may be of a plane type.

As regards the first multi-mode optical fiber 22, in one embodiment itis a so-called graded- index or gradient-index fiber (GIF), i.e., amulti-mode fiber on which the refractive index of the core, in additionto being higher than the refractive index of the cladding, follows agraded profile, and in particular is of a parabolic type. The outerdiameter of the first multi-mode optical fiber 22 may be larger than orequal to the outer diameter of the first single-mode optical fiber 20.

In greater detail, the first multi-mode optical fiber 22 is delimited bya further pair of facets, referred to hereinafter as the third facet F₃and the fourth facet F₄, respectively. The third facet F₃ is arranged incontact with the second facet F₂ of the first single-mode optical fiber20. In addition, in the embodiment illustrated in FIG. 2, the axes ofthe first single-mode optical fiber 20 and of the first multi-modeoptical fiber 22 coincide and consequently form a single axis H_(F),referred to hereinafter as the axis of the fiber H_(F).

In even greater detail, in a cross-section perpendicular to the axis ofthe first multi-mode optical fiber 22, the refractive index of the coreof the first multi-mode optical fiber 22 is, for example, directlyproportional to 1−(d/R)², where R is the radius of the core of the firstmulti-mode optical fiber 22 and d is the distance from the axis of thefiber.

In practice, the first multi-mode optical fiber 22 functions asso-called “selfoc lens” and is characterized by a corresponding pitchlength. As a function of the ratio existing between its own length andthe pitch length (or in any case an integer multiple of the pitchlength), the first multi-mode optical fiber 22 may generate at output afocused, a collimated, or a divergent beam, and further may enlarge orreduce the beam at input. For instance, assuming that in the firstmulti-mode optical fiber 22 there enters a generic beam with cylindricalsymmetry, denoting by P and L the pitch length and the length of thefirst multi-mode optical fiber 22, respectively, and limiting ourattention to considering the case L≤P, we find that: if ¼P<L<½ P, thebeam at output is focused; if L=¼ P, the beam at output is collimated;and if L<¼ P, the beam at output is divergent.

In practice, temporarily neglecting the question of the coupling betweenthe first laser diode 2 and the first single-mode optical fiber 20, itmay be found that the length of the first single-mode optical fiber 20is such that, at output from the second facet F₂, the first optical beamB₁ has a cylindrical symmetry, as a result of the symmetry of the firstsingle-mode optical fiber 20, in which it has propagated. In this way,at output from the first single-mode optical fiber 20, the first opticalbeam B₁ is substantially immune from the phenomenon of astigmatism. Froma quantitative standpoint, on the second facet F₂ of the firstsingle-mode optical fiber 20, the first optical beam B₁ has a diameterand a divergence that depend upon the first single-mode optical fiber20. For instance, the first optical beam B₁ may have, on the secondfacet F₂ of the first single-mode optical fiber 20, a diameter (at 1/e²)comprised between 3 μm and 8 μm; further, the first optical beam B₁ hasto a first approximation a spatial profile of a Gaussian type with abeam waist on the second facet F₂ (radius of the Gaussian beam at 1/e²)comprised, for example, between 1.5 μm and 4 μm. Then, the first opticalbeam B₁ interacts with the first multi-mode optical fiber 22, whichrenders it, for example, collimated.

As mentioned previously, the projective MEMS device 10 further comprisesthe first mobile structure 19, which is mobile with respect to the fixedstructure 17, to which it is coupled by using deformable elasticelements (not illustrated in FIG. 2) of semiconductor material.

In greater detail, whereas the first laser diode 2 is fixed to the fixedstructure 17, the first single-mode optical fiber 20 and the firstmulti-mode optical fiber 22 are, instead, coupled to the first mobilestructure 19, which may move, with respect to the fixed structure 17, indirections parallel to any one of the axes x, y, z. In particular, thefirst single-mode optical fiber 20, the first multi-mode optical fiber22, and the first mobile structure 19 are substantially fixed withrespect to one another and mobile with respect to the fixed structure17, and thus with respect to the first laser diode 2.

As described in greater detail hereinafter, the first mobile structure19 may be controlled electrically so as to vary the optical couplingbetween the first laser diode 2 and the first single-mode optical fiber20, and in particular between the front facet F_(a) of the first laserdiode 2 and the first facet F₁ of the first single-mode optical fiber20. In this connection, the first laser diode 2 is fixed to the fixedstructure 17 in a per se known manner, for example with techniques ofautomatic alignment that do not envisage turning-on of the first laserdiode 2. For instance, the fixed structure 17 may include a first metalpad 18 (made, for example, of gold or an alloy of tin and gold), fixedon which is the first laser diode 2, for example by a soldering processthat involves the bottom region (not illustrated) of the die 4 of thefirst laser diode 2. In this way, the first laser diode 2 is positionedwith a tolerance in the region of ±5 μm parallel to the axes x and y, aswell as with a tolerance in the region of ±3 μm parallel to the axis z.It is in any case possible to fix the first laser diode 2 to the fixedstructure 17 by using alternative techniques, such as for example byusing automatic image-recognition systems, or else usingthree-dimensional mechanical coupling structures. In the latter case, itis, for example, possible for the fixed structure 17 to formthree-dimensional coupling elements designed to couple mechanically tothe first laser diode 2 so as to constrain it with tolerances of ±1 μm.

As clarified hereinafter, by appropriately moving the first mobilestructure 19, it is thus possible to reduce the coupling losses betweenthe first laser diode 2 and the first single-mode optical fiber 20 sothat they fall within 1.5 dB. For instance, it is possible to get thegeometrical center O of the spot SP to lie along the axis of the fiberH_(F).

As shown in FIG. 3, the fixed structure 17 of the projective MEMS device10 comprises a cap 30 of semiconductor material (for example, silicon),a glass-frit region 32 and an epitaxial region 34, which is made ofsemiconductor material and in turn includes a first fixed epitaxialsub-region 36 and a second fixed epitaxial sub-region 37 and a mobileepitaxial sub-region 38.

The epitaxial region 34 delimits a cavity C, extending inside which isthe mobile epitaxial sub-region 38, which is arranged between the firstand second fixed epitaxial sub-regions 36, 37. As mentioned previouslyand as described in greater detail hereinafter, the mobile epitaxialsub-region 38 forms a suspended mass, which is connected to the fixedstructure 17 of the semiconductor support 16 (and thus also to the firstand second fixed epitaxial sub-regions 36, 37) through one or moreelastic semiconductor elements (designated by 100 in FIG. 4), whichfunction as springs and enable the mobile epitaxial sub-region 38, andthus the first mobile structure 19 to move with respect to the first andsecond fixed epitaxial sub-regions 36, 37, and more in general withrespect to the fixed structure 17, in the absence of blocking regionsdescribed hereinafter.

The glass-frit region 32 is arranged between the epitaxial region 34 andthe cap 30 so as to bond them together.

The fixed structure 17 further comprises a first dielectric region 40and a second dielectric region 44, made for example of TEOS oxide.

The first dielectric region 40 comprises a first fixed dielectric region41 and a first mobile dielectric region 42. The first fixed dielectricregion 41 overlies the first and second fixed epitaxial sub-regions 36,37, with which it is in direct contact. The first mobile dielectricregion 42 overlies the mobile epitaxial sub-region 38, with which it isin direct contact.

The second dielectric region 44 comprises a second fixed dielectricregion 46 and a second mobile dielectric region 48. The second fixeddielectric region 46 overlies the first fixed dielectric region 41, withwhich it is in direct contact. The second mobile dielectric region 48overlies the first mobile dielectric region 42, with which it is indirect contact.

The projective MEMS device 10 further comprises a substrate 50 ofsemiconductor material (for example, silicon), which includes a fixedportion 52 and a mobile portion 54. The fixed portion 52 extends overthe second fixed dielectric region 46, with which it is in directcontact, whereas the mobile portion 54 extends over the second mobiledielectric region 48, with which it is in direct contact. Furthermore,the mobile portion 54 is separated from the fixed portion 52 by a trenchT, which is in fluid communication with the underlying cavity C and hasan annular shape. In what follows, the trench T is referred to asinsulation trench T; further, in general it is assumed that the terms“annular” or “ring” do not necessarily imply a circular symmetry.

The projective MEMS device 10 further comprises a firstelectrical-connection region 60 and a second electrical-connectionregion 62, which are made of conductive material (for example,polysilicon) and extend through the first and second fixed dielectricregions 41, 46, until they contact the first and second fixed epitaxialsub-regions 36, 37, respectively. The projective MEMS device 10 furthercomprises an annular region 63, which surrounds, in direct contact, thefirst and second mobile dielectric regions 42, 48, and is physicallyseparated from the first and second dielectric regions 40, 44. Forinstance, the annular region 63 is made of polysilicon or else siliconnitride. The mobile portion 54 of the substrate 50 also overlies theannular region 63, with which it is in direct contact. As mentionedpreviously, in top plan view the annular region 63 does not necessarilyhave a circular symmetry and may thus have, for example, a polygonalshape.

The projective MEMS device 10 further includes a first through-siliconvia (TSV) and a second through-silicon via for providing electricalconnections. In particular, the embodiment illustrated in FIG. 3includes a first TSV 65 and a second TSV 67, which contact, respectivelythe first and second electrical-connection regions 60, 62. Furthermore,a second pad 68 and a third pad 70 of conductive material are present,which overlie respectively, in direct contact, the first and second TSVs65, 67 so as to enable electrical connection of the projective MEMSdevice 10 to the outside world, for example by a so-called wire bonding,in order to bias the first and second fixed epitaxial sub-regions 36,37.

In addition, the projective MEMS device 10 comprises a first blockingregion 72 and a second blocking region 74, which extend in correspondingseparate portions of the trench T. The first and second blocking regions72, 74 are made, for example, of a low-shrink adhesive material (forexample, a low-stress, low-shrink adhesive that may be opticallytreated), treated thermally, for the reasons described hereinafter.

As regards the cap 30, it has a cap surface, which faces the epitaxialregion 34 and is shaped so as to enable movement of the first mobilestructure 19 parallel to the axis y. For instance, the cap 30 may bedelimited at the top by a first cap surface (designated by S_(30a)),resting on which is the glass-frit region 32, and by a second capsurface S_(30b), arranged at a height lower than the height of the firstcap surface S_(30a), so that, as clarified hereinafter, the mobileepitaxial sub-region 38 may be located at a height lower than that ofthe first and second fixed epitaxial sub-regions 36, 37.

In greater detail, a top portion of the mobile portion 54 of thesubstrate 50 forms a groove G, which is for example V-shaped in a planeparallel to the plane yx and is designed to house at least a portion ofthe first single-mode optical fiber 20 and a portion of the firstmulti-mode optical fiber 22. In other words, the groove G functions asrecess designed to carry the first single-mode optical fiber 20 and thefirst multi-mode optical fiber 22; further, the groove G has alongitudinal axis parallel to the axis of the fiber H_(F). In addition,as mentioned previously, in the absence of the first and second blockingregions 72, 74, the first mobile structure 19 may move the firstsingle-mode optical fiber 20 and the first multi-mode optical fiber 22with respect to the first laser diode 2, which is fixed to the fixedstructure 17 since, in the absence of the first and second blockingregions 72, 74, the first mobile structure 19 is in fact mobile withrespect to the fixed structure 17.

As illustrated in greater detail in FIG. 4, and without any loss ofgenerality, the first fixed epitaxial sub-region 36 forms a first statorST1 and a second stator ST2. In turn, the first stator ST1 forms aplurality of elongated elements parallel to the direction x, referred toas the first stator elements 81, and the second stator ST2 forms aplurality of respective elongated elements parallel to the direction x,referred to as the second stator elements 82. Likewise, the second fixedepitaxial sub-region 37 forms a third stator ST3 and a fourth statorST4. In turn, the third stator ST3 forms a plurality of respectiveelongated elements parallel to the direction x, referred to as the thirdstator elements 83, and the fourth stator ST4 forms a plurality ofrespective elongated elements parallel to the direction x, referred toas the fourth stator elements 84. In addition, without any loss ofgenerality, the mobile epitaxial sub-region 38 has in top plan view theshape of a parallelepiped. Branching off from two sides of thisparallelepiped, opposite to one another and facing the first and secondfixed epitaxial sub-regions 36, 37, respectively, are a respective firstand second plurality of corresponding elongated elements parallel to theaxis x, referred to hereinafter as the first rotor elements 101 and thesecond rotor elements 102.

In greater detail, the first and second stator elements 81, 82 arespaced apart from one another and are arranged parallel to the axis z,in an alternating way. Likewise, the third and the fourth statorelements 83, 84 are spaced apart from one another and are arrangedparallel to the axis z, in an alternating way. Furthermore, the firstrotor elements 101 are comb-fingered with the elongated elements of thefirst fixed epitaxial sub-region 36, whereas the second rotor elements102 are comb-fingered with the elongated elements of the second fixedepitaxial sub-region 37. More in particular, at least one set of firstrotor elements 101 is present, each of which is arranged between acorresponding pair formed by a first stator element 81 and a secondstator element 82 adjacent to one another. Likewise at least one set ofsecond rotor elements 102 is present, each of which is arranged betweena corresponding pair formed by a third stator element 83 and a fourthstator element 84 adjacent to one another.

Once again with reference to the elastic semiconductor elements 100,without any loss of generality and in a way per se known manner, theyare connected indirectly to the first and second fixed epitaxialsub-regions 36, 37, i.e., they are connected mechanically to the latter,so that they may be set at a potential different from the potentials ofthe first and second fixed epitaxial sub-regions 36, 37.

In use, the mobile epitaxial sub-region 38 may be set at ground. Inaddition, if a positive voltage is applied to the third and fourthstator elements 83, 84, the mobile epitaxial sub-region 38 undergoes theaction of an electrostatic force that causes a translation thereof in adirection parallel and opposite to the axis x; likewise, if a positivevoltage is applied to the first and second stator elements 81, 82, themobile epitaxial sub-region 38 translates parallel to and in a directionconcordant with the axis x. If, instead, a positive voltage is appliedto the first and third stator elements 81, 83, the mobile epitaxialsub-region 38 translates parallel to and in a direction concordant withthe axis z. In addition, by applying a positive voltage on the secondand fourth stator elements 82, 84, the mobile epitaxial sub-region 38translates parallel to and in a direction discordant with respect to theaxis z.

As regards, instead, possible translations of the mobile epitaxialsub-region 38 parallel to the axis y, it is, for example, possible toconnect to ground the mobile epitaxial sub-region 38 and apply apositive or negative voltage to the cap 30, in which case the mobileepitaxial sub-region 38 translates parallel to the axis y, in thedirection of the cap.

In practice, the first and second epitaxial sub-regions 36, 37 and thefirst mobile structure 19 form a corresponding microelectromechanicalactuator designed to change the position of the first single-modeoptical fiber 20 and of the first multi-mode optical fiber 22 withrespect to the fixed structure 17, and thus with respect to the firstlaser diode 2. Furthermore, it may be shown that the first mobilestructure 19 may be moved with respect to the fixed structure 17 with anaccuracy of 0.1 μm, parallel to each of the axes x, y, z. Consequently,the first facet F₁ of the first single-mode optical fiber 22 may beshifted with respect to the front facet F_(a) with the aforesaidaccuracy.

The first laser diode 2, the first mobile structure 19, the firstsingle-mode optical fiber 20, and the first multi-mode optical fiber 22thus form a sort of first projective module M1, the axis of whichcoincides with the axis of the fiber H_(F). In addition, in the absenceof the first and second blocking regions 72, 73, it is possible to alignthe center of emission of the first laser diode 2 (i.e., the geometricalcenter O of the spot SP) to the axis of the fiber H_(F) with a toleranceof ±0.1 μm, thus optimizing the effectiveness of the optical coupling.Furthermore, at output from the first projective module, the firstoptical beam B₁ is substantially immune from astigmatism and possessesthe desired characteristics of collimation.

As illustrated in FIG. 5, the projective MEMS device 10 comprises asecond projective module M2 and a third projective module M3, which may,for example, be equal to the first projective module M1, but for thedifferences that will be mentioned hereinafter. Consequently, the secondprojective module M2 comprises, among other things, a second laser diode104, a second single-mode optical fiber 120, a second multi-mode opticalfiber 122, and a second mobile structure 119. Likewise, the thirdprojective module M3 comprises, among other things, a third laser diode204, a third single-mode optical fiber 220, a third multi-mode opticalfiber 222, and a third mobile structure 219. Mechanical coupling betweenthe fixed structure 17 and the second and third mobile structures 119,219 is obtained in the same way as what has been described as regardsthe first mobile structure 19 and in particular in connection with themobile epitaxial sub-region 38 and the first and second fixed epitaxialsub-regions 36, 37. Furthermore, each one of the first, second, andthird projective modules M1, M2, M3, and thus each one of thecorresponding mobile epitaxial sub-regions may be controlledindependently of the others. For instance, the pair formed by the firstand second fixed epitaxial sub-regions of each one of the first, second,and third projective modules M1, M2, M3 may be rendered electricallyindependent of the other two pairs.

As regards the aforementioned differences, the second laser diode 104emits electromagnetic radiation at a second wavelength λ₂ (for example,in the red, i.e., λ₂≈638 nm), referred to hereinafter as the secondoptical beam B₂. The third laser diode 204 emits electromagneticradiation with a third wavelength λ₃ (for example, in the green, i.e.,λ₃≈530 nm), referred to hereinafter as the third optical beam B₃.

The first, second, and third projective modules M1, M2, M3, and moreprecisely the respective multi-mode optical fibers, emit the first,second, and third optical beams B₁, B₂, B₃, respectively, so that theywill have substantially parallel axes of propagation.

In practice, and without any loss of generality, the projective MEMSdevice 10 is thus suited to forming a picoprojector of an RGB type.

As shown in FIG. 6, the projective MEMS device 10 further comprises anoptical device with dichroic behavior, referred to hereinafter as theoptical coupler 130.

The optical coupler 130 is of a per se known type and is mechanicallyfixed to the fixed structure 17 of the semiconductor support 16.Furthermore, the optical coupler 130 is designed to receive at input thefirst, second, and third optical beams B₁, B₂, B₃, which are spatiallyseparate, and to generate at output a fourth optical beam B₄. Inparticular, the fourth optical beam B₄ is given by the spatialsuperposition of the first, second, and third optical beams B₁, B₂, B₃,the axes of which, at output from the optical coupler 130, substantiallycoincide. The output of the optical coupler 130 thus forms theaforementioned common output.

In practice, the optical coupler 130 functions as a so-called“wavelength-division multiplexer” (WDM); further, before impinging uponthe optical coupler 130, the first, second, and third optical beams B₁,B₂, B₃ propagate in air.

As shown once again in FIG. 6, the projective MEMS device 10 furthercomprises a fourth multi-mode optical fiber 132 and a fifth multi-modeoptical fiber 134, as well as a lens 136. There are, however, possibleembodiments in which one or more of the fourth multi-mode optical fiber132, the fifth multi-mode optical fiber 134, and the lens 136 areabsent.

The fourth multi-mode optical fiber 132 has a core with constantrefractive index (i.e., not graded) and is designed to receive thefourth optical beam B₄, after the latter has been emitted by the opticalcoupler 130 and has propagated for a stretch in air. Furthermore, thefourth multi-mode optical fiber 132 performs the task of aligningfurther the propagation of the optical beams and reducing possibleresidual misalignments present between the first, second, and thirdoptical beams B₁, B₂, B₃ at output from the optical coupler 130. Forinstance, the fourth multi-mode optical fiber 132 has a length comprisedbetween 300 μm and 1000 μm.

The fifth multi-mode optical fiber 134 has a core with graded refractiveindex; in particular, the refractive index has a parabolic profile. Forinstance, the fifth multi-mode optical fiber 134 has a length comprisedbetween 200 μm and 1000 μm; further, the input facet of the fifthmulti-mode optical fiber 134 is, for example, arranged in contact withthe output facet of the fourth multi-mode optical fiber 132. The fifthmulti-mode optical fiber 134 performs the function of adapting thedivergence of the fourth optical beam B₄ as a function of the opticalcomponents (for example, mirrors for carrying out scanning) of apicoprojector that incorporates the projective MEMS device 10, theseoptical components being arranged downstream of the latter.

The lens 136 is arranged downstream of the fifth multi-mode opticalfiber 134 and may form the lens of the projective MEMS device 10, orelse the lens of the picoprojector that incorporates the projective MEMSdevice 10.

In general, irrespective of the components arranged downstream of theoptical coupler 130, the lengths of the multi-mode optical fibers ofeach one of the first, second, and third projective modules M1, M2, M3may be determined, for example, on the basis of a desired beam waist ona screen arranged at a given distance. In this case, it is possible tocalculate the corresponding beam waist on the mirrors of thepicoprojector (comprised, for example, between 500 μm and 1000 μm). Thenthe divergence and size of each optical beam generated by eachprojective module is determined as a function of the distance of eachmulti-mode optical fiber from the mirrors and of the optical pathfollowed by the corresponding optical beam. For standard applications,the optical beams—may exit substantially collimated from the multi-modefibers of the corresponding projective modules.

As illustrated in FIG. 7, the projective MEMS device 10 may in fact forma projective MEMS system (i.e., a picoprojector) 300, which furtherincludes at least one mirror 302 (for example, of a MEMS type) designedto receive the fourth optical beam B₄ and to change the direction ofpropagation thereof for scanning an area. Albeit not shown, theprojective MEMS system 300 may further include driving circuits designedto change the intensity of the first, second, and third optical beamsB₁, B₂, B₃.

The projective MEMS system 300 may be a separate accessory, which may bemechanically and electrically coupled to a portable electronic apparatus400, such as for example a cellphone or smartphone (or else, forexample, a PDA, a tablet, a digital audio player, or a controller forvideo games). In this case, the projective MEMS system 300 is providedwith an own casing 303, which has at least one portion 306 transparentto the fourth optical beam B₄, reflected by the mirror 302. The casing303 of the projective MEMS system 300 is releasably coupled to a casing403 of the portable electronic apparatus 400.

Alternatively, as illustrated in FIG. 8, the projective MEMS system 300may be integrated within the portable electronic apparatus 400, beingarranged inside the casing 403 of the portable electronic apparatus 400itself, which has in this case a respective portion 406 transparent tothe fourth optical beam B₄ reflected by the mirror 302. In this case,the projective MEMS system 300 is, for example, coupled to a printedcircuit present within the casing 403 of the portable electronicapparatus 400.

The present projective MEMS device may be manufactured by carrying outthe process described hereinafter, which refers to an embodimentslightly different from the one shown in FIG. 3, as pointed out at theend of the description of the process. In addition, the ensuingdescription is limited to the steps of manufacture of the firstprojective module M1, located in a portion of a microelectronicstructure 500; these steps also involve other portions of themicroelectronic structure 500, for leading to formation also of thesecond and third projective modules M2, M3.

In detail, as illustrated in FIG. 9, there is provided themicroelectronic structure 500, which comprises the substrate 50 ofsemiconductor material, which has, for example, a thickness of 400 μm,and the first and second dielectric regions 40, 44, which haverespective thicknesses for example of 2 μm and 1.5 μm. In what follows,referred to as bottom surface S_(inf) and top surface S_(sup) of thesubstrate 50 are the surfaces that, in this step of the manufacturingprocess, delimit the substrate 50 at the bottom and at the top,respectively, even though then, once the projective MEMS device 10 iscompleted, these surface are reversed. This having been said, the seconddielectric region 44 is arranged on top of the top surface S_(sup).

The first dielectric region 40 is arranged on top of the seconddielectric region 44. Furthermore, the first dielectric region 40includes the first fixed dielectric region 41 and the first mobiledielectric region 42. The second dielectric region 44 includes thesecond fixed dielectric region 46 and the second mobile dielectricregion 48. Furthermore, the microelectronic structure 500 comprises thefirst and second electrical-connection regions 60, 62 and the annularregion 63. In addition, the microelectronic structure 500 comprises afirst sacrificial region 502 and a second sacrificial region 504, formedby the first and second dielectric regions 40, 44, respectively.Consequently, the first sacrificial region 502 is arranged on top of,and in direct contact with, the second sacrificial region 504. Inparticular, the first and second sacrificial regions 502, 504 have anannular shape and are arranged between the annular region 63, with whichthey are in direct contact, and the first and secondelectrical-connection regions 60, 62.

The microelectronic structure 500 further comprises the epitaxial region34, which has a thickness comprised, for example, between 20 μm and 30μm. In particular, the microelectronic structure 500 comprises the firstand second fixed epitaxial sub-regions 36, 37. The first fixed epitaxialsub-region 36 overlies the first fixed dielectric region 41, the firstelectrical-connection region 60, and a first peripheral part of thefirst sacrificial portion 502. The second fixed epitaxial sub-region 37overlies the first fixed dielectric region 41, the secondelectrical-connection region 62, and a second peripheral part of thefirst sacrificial portion 502.

The microelectronic structure 500 further comprises the mobile epitaxialsub-region 38, which is separated from the first and second fixedepitaxial sub-regions 36, 37 by a corresponding pair of trenches(designated by 506 and 508, respectively), referred to hereinafter asthe first patterning trench 506 and the second patterning trench 506,508, respectively. Albeit not visible in FIG. 9, also the elasticsemiconductor elements 100 are already present. The mobile epitaxialsub-region 38 is, however, fixed with respect to the substrate 50 and tothe first and second fixed epitaxial sub-regions 36, 37 on account ofthe presence of the first and second sacrificial regions 502, 504, whichrigidly connect the mobile epitaxial sub-region 38 to the first andsecond fixed epitaxial sub-regions 36, 37.

Next, as illustrated in FIG. 10, a wet etch is carried out using, forexample, hydrofluoric acid (HF) for removing portions of the first andsecond sacrificial regions 502, 504 arranged underneath the first andsecond patterning trenches 506, 508, substantially without affecting theepitaxial region 34. During etching, the annular region 63 protects thefirst and second mobile dielectric regions 42, 48 and forms with thelatter a sort of permanent-connection region, which connects the mobileepitaxial sub-region 38 to an underlying portion of the substrate 50. Inthe example illustrated in FIG. 10, the etch is such that the annularregion 63 is exposed, whereas residual portions of the first and secondsacrificial regions 502, 504, arranged in contact with the first andsecond electrical-connection regions 60, 62, respectively, remain andconcur to forming, respectively, the first and second fixed dielectricregions 41, 46.

At the end of the operations illustrated in FIG. 10, the annular region63 is surrounded by a cavity 510, referred to hereinafter as the processcavity 510. The process cavity 510 has a closed shape in top plan view.

Next, as shown in FIG. 11, an operation of wafer-to-wafer bonding iscarried out for fixing the cap 30 to the first and second fixeddielectric regions 36, 37, by interposition of the glass-frit region 32.

Next, as shown in FIG. 12, the microelectronic structure 500 is turnedover and formed on the bottom surface S_(inf) are the first pad (notillustrated in FIG. 12) and the second and third pads 68, 70.

Next, as illustrated in FIG. 13, a process is carried out ofphotolithography and subsequent wet etching (for example, usingpotassium hydroxide, KOH) of the bottom surface S_(inf) of the substrate50 for removing selectively portions of the latter. In this way, aplurality of recesses is formed on the bottom surface S_(inf).

In the example illustrated in FIG. 13, a first recess 531 is formed,elongated parallel to the axis z and having, in a plane perpendicular tothe axis z, the shape of a isosceles trapezium, with minor base andsides formed by the substrate 50. More in particular, the minor base isparallel to the bottom surface S_(inf), whereas the sides aretransverse, but not perpendicular, with respect to the bottom surfaceS_(inf).

In addition, a second recess 532 is formed, which, in top plan view, hasan annular (and thus, closed and hollow) shape and surrounds the firstrecess 531. Likewise formed are a third recess 533 and a fourth recess534, each of which has an annular shape, in top plan view, and surroundsthe second and third pads 68, 70, respectively. In the exampleillustrated in FIG. 13, also the second, third, and fourth recesses 532,533, 534 locally have cross-sections equal to the aforementionedtrapezoidal cross-section of the first recess 531, even though this isnot necessary for the purposes of the present disclosure. More ingeneral, one or more of the first, second, third, and fourth recesses531, 532, 533, 534 may have different shapes; for example, the firstrecess 531 may have a triangular cross-section. In general, the recessesmay have shapes and depths different from one another.

Next, as illustrated in FIG. 14, formed on the bottom surface S_(inf)and within the recesses is a protective layer 550, of a conformabletype, thus with a uniform thickness. This protective layer 550 isformed, for example, by a resist, which is sprayed on themicroelectronic structure 500, thus coating also the bottom walls andside walls of the first, second, third, and fourth recesses 531, 532,533 and 534.

Next, as shown in FIG. 15, portions of the protective layer 550 arrangedon the bottom walls of the second, third, and fourth recesses 532, 533,534 are selectively removed, with photolithographic techniques. In thisway, on the bottom of the second, third, and fourth recesses 532, 533,534, a first window 542, a second window 543, and a third window 544through the protective layer 550 are, respectively, formed, thusexposing corresponding portions of the substrate 50. Also the first,second, and third windows 542, 543, 544 have an annular shape in topplan view. Furthermore, the first window 542 may be such that portionsof the first and second patterning trenches 506, 508 are verticallyaligned with respect to portions of the overlying first window 542.

Next, as illustrated in FIG. 16, a DRIE (Deep Reactive-Ion Etch) iscarried out through the first, second, and third windows 542, 543, 544for removing the underlying portions of substrate 50 entirely. Ingreater detail, this operation leads to formation of the first andsecond TSVs 65, 67, as well as of the insulation trench T, which is influid communication with the process cavity 510 and with the first andsecond patterning trenches 506, 508. In addition, this operation leadsto formation of the fixed portion 52 and the mobile portion 54 of thesubstrate 50. In particular, the insulation trench T insulates themobile portion 54 of the substrate 50 from the fixed portion 52, themobile portion 54 being formed by the portion of substrate 50 connectedto the mobile epitaxial sub-region 38 through, among other things, thefirst and second mobile dielectric regions 42, 48.

In practice, the operations illustrated in FIG. 16 enable release of thefirst mobile structure 19 with respect to the fixed structure 17 towhich it is connected by the aforementioned elastic semiconductorelements 100, and more precisely render them mobile with respect to oneanother. Further, since the second, third, and fourth recesses 532, 533and 534 have a same depth, calibration and execution of the DRIE arefacilitated, since, underneath the first, second, and third windows 542,543, 544, always the same thickness of semiconductor material isremoved.

Next, as shown in FIG. 17, the remaining portions of the protectivelayer 550 are removed, and the first single-mode fiber 20 and the firstmulti-mode fiber 22 (which is not visible in FIG. 17) are arranged inthe first recess 531. In this connection, the embodiment illustrated inFIG. 17 differs from the one illustrated in FIG. 3 in that the firstrecess 531, which is functionally equivalent to the groove G shown inFIG. 3, has a trapezoidal cross-section, instead of a triangular one.

Next, after fixing the first laser diode 2 has been fixed to the fixedstructure 17, the first mobile structure 19 is moved as describedpreviously, so as to locate the point in which the first optical beam B₄has, at output from the first multi-mode optical fiber 22, the maximumintensity. This condition is shown, purely by way of example, in FIG.18. Then, in a way not illustrated, the first and second blockingregions 72, 74 are formed within the insulation trench T. The first andsecond blocking regions 72, 74 fix the mobile portion 54 of thesubstrate 52 to the fixed portion 52, thus preventing any furthermovement of the first mobile structure 19 with respect to the fixedstructure 17. In practice, the first and second blocking regions 72, 74make it possible to maintain the arrangement that guarantees maximumcoupling efficiency between the first laser diode 2 and the firstsingle-mode optical fiber 20.

In general, the operations of movement of the first, second, and thirdmobile structures 19, 119, 219 in order to optimize the opticalcouplings may be carried out at different times, as likewise formationof the corresponding pairs of blocking regions.

From what has been described and illustrated previously, the advantagesthat the present solution affords emerge clearly.

In particular, the present projective MEMS device enables generation ofan optical beam for applications of the flying spot type that issubstantially immune from the phenomenon of astigmatism and with anoptimized intensity, at the same time maintaining small overalldimensions. Possibly, also the collimation characteristics may beoptimized.

In conclusion, it is clear that modifications and variations may be madeto what has been described and illustrated herein, without therebydeparting from the scope of the present disclosure.

For instance, the structure of each laser diode may be different fromwhat has been described. In particular, the number, arrangement, shape,and composition of the layers of each laser diode (not described indetail, in so far as they are not relevant for the purposes of thepresent disclosure), and thus of the corresponding die, may be of anytype. Furthermore, one or both of the facets of each laser diode may beformed by corresponding structures designed to guarantee that the facetshave desired values of reflectivity; for example, the front facet F_(a)of each laser diode may be formed by an anti-reflective structureintegrated with the corresponding die.

It is further possible for the number of the laser diodes and/or theirrespective wavelengths to be different from what has been described.

In addition, one or more of the projective modules may be without thecorresponding multi-mode optical fiber. Furthermore, one or more of theoptical fibers mentioned may (for example) be of the type with aplurality of claddings.

As regards the conditions of alignment of the axes (for example, theaxes of the single-mode optical fiber and of the multi-mode opticalfiber of a same projective module), limited misalignments are possibleof the order of microns, as also between the axes of the fibers ofdifferent projective modules (also in this case, of the order ofmicrons). On the other hand, given the small lengths of the fibersmentioned, it is likewise possible for one or more fibers to havelocally a non-infinite radius of curvature. In this case, assuming forexample the presence of a curved single-mode fiber, the coupling withthe corresponding laser diode may be obtained by trying to align thecenter of emission of the corresponding laser with the point given bythe intersection of the (curved) axis of symmetry of the optical fiberwith the facet of the optical fiber facing this corresponding laser.

Further possible are embodiments comprising elements additional to whathas been described. For instance, one or more of the facets of thefibers described (for example, the first facet F₁ of the firstsingle-mode optical fiber 20) may be coated with an anti-reflectivelayer. One or more fibers may be partially metallized, to enablesoldering thereof. Furthermore, as regards the first single-mode fiberof at least one projective module, it may be of a non-lensed type, inwhich case the first facet F₁ is plane. In this case, between the firstfacet F₁ and the front facet F_(a) of the corresponding die there a lensmay be inserted (for example, a hemispherical one) so as to guarantee inany case a good optical coupling. More in general, embodiments arepossible (not illustrated) in which, in each projective module, insteadof the corresponding single-mode optical fiber, a correspondingmulti-mode optical fiber is present, for example of a step-index type.These embodiments are suited to applications of a LIDAR type, since inthese applications maximization of the transmitted power is privilegedover resolution of the pixel or reduction of astigmatism.

As regards the annular region 63 and each of the elements referred tothat have an annular shape, this shape may be of any type (for example,circular or polygonal, in top plan view).

As regards the first rotor elements 101, the second rotor elements 102,and the first, second, third, and fourth stator elements 81, 82, 83, 84,they may have shapes and arrangements different from what has beendescribed.

Finally, as regards the manufacturing process, it is possible for therecesses obtained (illustrated for example in FIG. 13) not to have alleither a same shape or a same depth, as mentioned previously.

In addition, embodiments are possible in which the annular region 63 isabsent. In this case, the wet etch mentioned with reference to FIG. 10is carried out with times such as to prevent complete removal of thefirst and second mobile dielectric regions 42, 48 so as to prevent themobile epitaxial sub-region 38 from mechanically decoupling from thesubstrate 50.

The various embodiments described above can be combined to providefurther embodiments. These and other changes can be made to theembodiments in light of the above-detailed description. In general, inthe following claims, the terms used should not be construed to limitthe claims to the specific embodiments disclosed in the specificationand the claims, but should be construed to include all possibleembodiments along with the full scope of equivalents to which suchclaims are entitled. Accordingly, the claims are not limited by thedisclosure.

1. A projective MEMS device, comprising: a fixed supporting structuremade at least in part of semiconductor material; and a number ofprojective modules, each projective module including: an optical sourcefixed to the fixed supporting structure; a microelectromechanicalactuator including a mobile structure, said microelectromechanicalactuator being configured to vary a position of said mobile structurewith respect to the fixed supporting structure; and a first opticalfiber mechanically coupled to said mobile structure and configured tooptically couple to said optical source according to the position ofsaid mobile structure; and at least one elastically deformable elementmechanically coupling each mobile structure to the fixed supportingstructure, wherein: the microelectromechanical actuator of eachprojective module further comprises a fixed region of semiconductormaterial, fixed to said fixed supporting structure; the mobile structureof each microelectromechanical actuator comprises a mobile region ofsemiconductor material, which is mechanically coupled to the fixedsupporting structure by the at least one elastically deformable element;and the fixed region and the mobile region of each projective module areconfigured to be electrically controlled so as to vary the position ofthe mobile region with respect to the fixed region.
 2. The deviceaccording to claim 1, wherein the first optical fiber of each projectivemodule is a single-mode optical fiber.
 3. The device according to claim1, wherein the optical source of each of said projective modules is abare-chip optical source.
 4. The device according to claim 1, whereinthe mobile structure of each microelectromechanical actuator furthercomprises: a front region of semiconductor material, configured to carrythe corresponding initial optical fiber; and an intermediate regionarranged between the front region and the mobile region and configuredto keep the front region and the mobile region fixed together.
 5. Thedevice according to claim 4, wherein said intermediate region comprisesan inner portion of dielectric material and an outer portion ofpolysilicon or silicon nitride, which laterally surrounds the innerportion.
 6. The device according to claim 4, wherein said fixed regionand said mobile region of each microelectromechanical actuator comprisecorresponding comb-fingered elongated elements.
 7. The device accordingto claim 1, wherein each projective module further comprises a secondoptical fiber of a multi-mode type and with a graded refractive index,said second optical fiber being arranged downstream of the correspondingfirst optical fiber, said second optical fiber being further opticallycoupled to said corresponding first optical fiber and being mechanicallycoupled to the corresponding mobile structure, and wherein the mobilestructure of each microelectromechanical actuator further comprises: afront region of semiconductor material, configured to carry thecorresponding first optical fiber and the corresponding second opticalfiber; and an intermediate region, which is arranged between the frontregion and the mobile region and is configured to keep the front regionand the mobile region fixed together.
 8. The device according to claim1, further comprising a cap of semiconductor material; and wherein themobile region of each microelectromechanical actuator overlies, at adistance, said cap and is configured to be biased at a voltage differentfrom a voltage of said cap.
 9. The device according to claim 1, whereinthe optical sources of said number of projective modules are configuredto generate respective input optical beams that are spatially arrangedat a distance apart from each other, said device further comprising adichroic optical structure mechanically coupled to said fixed supportingstructure and configured to receive said input optical beams and tosuperimpose the input optical beams spatially for forming substantiallya single output optical beam.
 10. The device according to claim 1,wherein each first optical fiber has a facet facing the correspondingoptical source, said facet forming a lens configured to increase acoupling coefficient between said corresponding optical source and saidfirst optical fiber.
 11. The device according to claim 1, wherein saidnumber of projective modules is equal to three, and include threeoptical sources configured to generate red, green, and blue visibleelectromagnetic radiation, respectively.
 12. The device according toclaim 1, wherein each projective module comprises at least one blockingregion configured to fix the position of the mobile structure of therespective microelectromechanical actuator with respect to the fixedsupporting structure.
 13. A method for manufacturing a projective MEMSdevice, comprising: forming a fixed supporting structure made at leastin part of semiconductor material; and forming a number of projectivemodules, said forming the number of projective modules includes, foreach projective module: forming a corresponding microelectromechanicalactuator that includes a respective mobile structure and is configuredto vary a position of said mobile structure with respect to the fixedsupporting structure; fixing a corresponding optical source to the fixedsupporting structure; and mechanically coupling the mobile structure ofthe corresponding microelectromechanical actuator to a first opticalfiber configured to be optically coupled to the corresponding opticalsource according to the position of said mobile structure.
 14. Themethod according to claim 13, wherein forming the number of projectivemodules includes: forming a microelectronic structure including: asubstrate of semiconductor material, including a first surface and asecond surface; an intermediate dielectric region which contacts thesecond surface of the substrate; and a patterned epitaxial region ofsemiconductor material, which contacts the intermediate dielectricregion and includes a mobile region and at least one fixed regionmechanically coupled together by a number of elastically deformableelements; wherein said intermediate dielectric region includes: asacrificial portion which rigidly connects the mobile region to thefixed region; and a connection portion which connects the mobile regionto the substrate; selectively removing said sacrificial portion of theintermediate dielectric region; mechanically coupling a cap ofsemiconductor material to said fixed region of the patterned epitaxialregion; turning over the microelectronic structure; and selectivelyremoving portions of the substrate that extend from the first surface asfar as the second surface, thereby forming a trench that delimits amobile portion of the substrate, which is fixed to said connectionportion of the intermediate dielectric region.
 15. The method accordingto claim 14, further comprising forming, by a wet etch, at least onefirst recess in said mobile portion of the substrate, said first recessextending from the first surface and being configured to house at leastpart of the initial optical fiber.
 16. The method according to claim 15,wherein selectively removing portions of the substrate comprises formingat least one second recess by said wet etch, and subsequently carryingout a DRIE etch starting from a bottom of said second recess.
 17. Themethod according to claim 16, further comprising at least one thirdrecess having an annular shape by said wet etch, and subsequently, bysaid DRIE etch, removing a portion of a part of substrate different fromsaid mobile portion, said portion of a part of substrate extending froma bottom of said third recess as far as the second surface so as to forma TSV.
 18. A projective MEMS device, comprising: a fixed supportingstructure made at least in part of semiconductor material; and a numberof projective modules, each projective module including: an opticalsource fixed to the fixed supporting structure; a microelectromechanicalactuator including a mobile structure, said microelectromechanicalactuator being configured to vary a position of said mobile structurewith respect to the fixed supporting structure; and a first opticalfiber mechanically coupled to said mobile structure and configured tooptically couple to said optical source according to the position ofsaid mobile structure, wherein the optical sources of said number ofprojective modules are configured to generate respective input opticalbeams that are spatially arranged at a distance apart from each other;and a dichroic optical structure mechanically coupled to said fixedsupporting structure and configured to receive said input optical beamsand to superimpose the input optical beams spatially for formingsubstantially a single output optical beam.
 19. A projective MEMSdevice, comprising: a fixed supporting structure made at least in partof semiconductor material; and a number of projective modules, eachprojective module including: an optical source fixed to the fixedsupporting structure; a microelectromechanical actuator including amobile structure, said microelectromechanical actuator being configuredto vary a position of said mobile structure with respect to the fixedsupporting structure; and a first optical fiber mechanically coupled tosaid mobile structure and configured to optically couple to said opticalsource according to the position of said mobile structure, wherein eachfirst optical fiber has a facet facing the corresponding optical source,said facet forming a lens configured to increase a coupling coefficientbetween said corresponding optical source and said first optical fiber.20. A projective MEMS device, comprising: a fixed supporting structuremade at least in part of semiconductor material; and a number ofprojective modules, each projective module including: an optical sourcefixed to the fixed supporting structure; a microelectromechanicalactuator including a mobile structure, said microelectromechanicalactuator being configured to vary a position of said mobile structurewith respect to the fixed supporting structure; and a first opticalfiber mechanically coupled to said mobile structure and configured tooptically couple to said optical source according to the position ofsaid mobile structure, wherein each projective module comprises at leastone blocking region configured to fix the position of the mobilestructure of the respective microelectromechanical actuator with respectto the fixed supporting structure.